Process for driving the exciting coil of an electromagnetically driven reciprocating piston pump

ABSTRACT

A method for signalling an energizing coil of a solenoid-operated reciprocating plunger pump employed as a fuel injection device, in which the energizing coil is energized via a current control circuit pulsed at high-frequency by an energizing current and each pulse causes an impulse movement of an armature driven by the energizing coil, and the current control circuit controls the energizing current flowing through the energizing coil as a function of a current setpoint curve, each pulse of the current setpoint curve comprises a gradually rising leading edge resulting in a corresponding gradually rising leading edge of the pulse of the energizing current in the energizing coil, the current setpoint curve being controlled so that the energizing current does not change faster than the maximum change in current possible for the minimum voltage available at the energizing coil and limited due to mutual induction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for signalling an energizing coil of asolenoid-operated reciprocating plunger pump as set forth in thepreamble of claim 1.

2. Description of Related Art Including Information Disclosed Under 37CFR 1.97 and 1.98

One such method of signalling an energizing coil of a solenoid-operatedreciprocating plunger pump is known from PCT/EP 93/00494. In this methoda current control circuit is employed which controls the energizingcurrent flowing through the energizing coil 600 (FIG. 1) as a functionof the current setpoint in the form of a current or voltage setting. Theenergizing coil 600 is connected to a power transistor 601 which isconnected to ground via a precision resistor 602, a comparator 602 beingconnected by its output to the control input of the transistor 601, forexample, to the base of the transistor. The non-inverting input of thecomparator 603 receives the current setpoint, obtained for example bymeans of a microcomputer. The inverting input of the comparator 603 isconnected to one side of a resistor which is connected to the transistor601. This circuit is a bang-bang control system which limits the currentflowing through the energizing coil as a maximim, depending on theapplied current setpoint, ON/OFF action of the power transistor 601chopping roughly delta-shaped the current flow through the energizingcoil in the control range.

In this application of the method the current setpoint is applied in theform of square wave pulses to the comparator 603, the length of thepulses dictating the duration of the corresponding energizing pulse andthe amplitude of the pulse dictating the maximum current flowing throughthe energizing coil.

By this method different amounts of fuel can be metered by thereciprocating plunger pump operating more or less independently of coilheating and fluctuations in the supply voltage.

From DE 28 41 781 C2 a means for operating electromagnetic devices ininternal combustion engines, more particularly solenoid valves in fuelsupply systems, is known. This means controls the current profile of aninjection signal at the start of the injection pulse to an excessivelyhigh value ensuring that the solenoid valve is opened and holds thecurrent constant at a value slightly below the peak value attained atthe start.

In DE 37 22 527 A1 a method of signalling an injector for an internalcombustion engine is described in which the energizing coil of theinjector is signalled in a way similar to the method as described in DE28 41 781 C2, whereby, however, at the end of the injection pulse atransition is made from a chopped current regulation, during which thecurrent value oscillates between two threshold values, to a currentregulation having a constant current value so that the injector isclosed at a precisely predetermined point in time in OFF action, i.e. atthe end of the current pulse.

SUMMARY OF THE INVENTION

It is the object of the invention to sophisticate the method cited atthe outset so that an amount of fuel injected per injection pulse can bemetered highly exactly and achieving this independently of coil heatingor fluctuations in the supply voltage.

This object is achieved by a method having the features as set forth inclaim 1. Advantageous aspects of the invention are characterized in thesub-claims.

The invention is based on the following findings:

Due to the self-induction in the energizing coil the energizing currentfails to directly increase to the maximum strength, instead eachenergizing current pulse 94 features a leading edge 95 which isproportional to an exponential function (FIG. 2). The slope of theleading edge 95, or the change in current in the energizing coil, is adirect function of the voltage applied to the coil which, in motorvehicles, may greatly depend on changes in load, as is known. On top ofthis the resistance in the energizing coil alters as a function ofchanges in temperature so that the leading edges actually occuringdiffer in slope.

The integral over such an energizing current pulse is roughlyproportional to the amount of fuel injected by the fuel injection deviceper injection pulse, the leading edges 95 significantly influencing theamount of fuel injected per injection pulse so that the differences inthe leading edges result in considerably differing amounts of fuelinjected.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail with respect to thedrawing in which:

FIG. 1 is a circuit diagram of a current control circuit,

FIG. 2 is a diagram showing the pulse profile of the energizing coilcurrent in accordance with the method known from PCT/EP 93/00494,

FIG. 3 is an example illustration of a fuel injection device,

FIG. 4 is a diagram schematically plotting the energizing currenti_(sp), the armature stroke s and the injection pressure p as a functionof time t,

FIG. 5 is a diagram plotting the force F exerted by an armature drivenby the energizing coil as a function of a working air gap 1 in thesolenoid-operated fuel injection device,

FIG. 6 is a diagram illustrating the pulse profile of the energizingcurrent by the method in accordance with the invention,

FIG. 7 is a diagram showing the pulse profile of the energizing currentadapted to the characteristics of the fuel injection device as shown inFIG. 3,

FIG. 8 is a diagram of a circuit in accordance with the invention forgenerating a current setpoint curve for a current control circuit, and

FIGS. 9a and 9b are diagrams illustrating the current setpoint curveachieved by the circuits shown in FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

In the method in accordance with the invention a current control circuitis used, as is known, for example, from PCT/EP 93 00494 (FIG. 1) tocontrol the current in an energizing coil of a solenoid-operatedreciprocating plunger pump used as a fuel injection device. Theenergizing coil is excited by high-frequency pulses, each pulseresulting in an abrupt movement of an armature operated by theenergizing coil. The current control circuit controls the energizingcurrent as a function of a current setpoint applied pulsed.

In accordance with the invention each pulse of the current setpoint issignalled by a gradually rising leading edge resulting in acorrespondingly gradually rising leading edge in the pulse of theenergizing current in the energizing coil, whereby the change in theenergizing current is no quicker than as permitted by the maximum changein current limited by the mutual induction in the energizing coilpossible for the minimum voltage available.

The maximum change in current for the voltage available as a minimum isthe change in current resulting if the voltage available as a minimumdue to fluctuations in load and temperature were to be applied directlyto the energizing coil, and the increase in current in the energizingcoil were to be limited by the mutual induction due to the inductance ofthe energizing coil.

By the method in accordance with the invention a current setpoint curve90 is set at the input of the current control circuit, resulting in acorresponding energizing current 91 in the energizing coil (FIG. 6). Theprofile of the current setpoint curve 90 is selected so that theresulting energizing current 91 is always in the regulating range of thecurrent control circuit, i.e. the increase in the current setpoint curve90 is smaller than the maximum change in current at which the voltageavailable at the energizing coil is at a minimum. As explained above,this voltage may greatly vary, depending on temperature and engine load.

Preferably the profile of the current setpoint curve 90 is below that ofa corresponding current curve 92 having a maximum increase for thevoltage available at the energizing coil as a minimum. Since the currentcurve 92 obeys an exponential function due to the mutual induction ofthe energizing coil 9, 600 (FIG. 1, FIG. 3) it is expedient when theprofile of the leading edge of the current setpoint curve 90 is suchthat it roughly also corresponds to such an exponential function and canbe represented by the following equations

    i.sub.sp =I.sub.0 -e.sup.-at I.sub.0                       (1)

    u.sub.sp =U.sub.0 -e.sup.-at U.sub.0                       (2)

where I₀ and U₀ respectively are base values and a is a parameter to bedetermined.

Preferably the engine speed and/or the temperature existing at theenergizing coil is sensed so that the voltage available at theenergizing coil can be determined or the voltage available as a minimumcan be estimated to enable the current setpoint curve 90 to be adaptedto the voltage conditions actually existing. Adapting in this way isdone, for example, by changing the base values or the parameter a.

In adapting the current setpoint curve to the engine conditions it needsto be taken into account that at low speeds of the alternator only avery small voltage is furnished, but the injection actions are spacedaway from each other far in time so that the injection action can becontrolled with relatively long pulses at low current, whereas at highengine speeds the time available for the injection action becomessmaller all the time, this being the reason why the pulses need to beshortened, whereby due to a higher minimum voltage being available,however, a larger current can be applied to the energizing coil.

The current setpoint curve can be computed by means of a microprocessor,for example, as a function of the crank angle position and applied tothe input of the current control circuit as the setting current orsetting voltage by a digital/analog converter or by means of pulse-widthmodulation.

This method is put to use preferably in a pump-injector device as isknown, for example, from DD-PS 120 514, from DD-PS 213 472, from DE-OS23 07 435 or from EP 0 629 265.

One such pump-injector device, based on the solid-state energy storageprinciple, is illustrated in FIG. 3. In this fuel injection device aninitial partial stroke of the delivery element of the injection pump isprovided in which the displacement of the fuel results in no pressurebeing built up, whereby the partial stroke of the delivery elementserving to store energy is determined expediently by a storage volumee.g. in the form of a vacant volume and a stop element, both of whichcan be configured differingly and which permit displacement of the fuelin response to a stroke travel "X" of the delivery element of thereciprocating plunger pump. It is not until the displacement of the fuelis suddenly discontinued that pressure is built up in the fuel abruptlyso that displacement of the fuel in the direction of the injector iscaused.

The injection device as shown in FIG. 3 comprises a solenoid-operatedreciprocating plunger pump 1 connected via a delivery line 2 to aninjector 3. Branching off from the delivery line 2 is a suction line 4which is in connection with a fuel reservoir 5 (tank). In addition, avolume storage element 6 is connected via a conduit 7 to the deliveryline 2 roughly in the region of the connection of the suction line 4.

The pump 1 is configured as a reciprocating plunger pump and has a body8 in which a solenoid coil 9 is mounted, an armature 10 arranged in theregion of the coil passage, this armature being configured as acylindrical body, for example, as a solid body and guided in a pump bodybore 11 located in the region of the longitudinal centerline of the ringcoil 9 where it is urged into its starting position by means of acompression spring 12, it being in connection with the bottom 11a of thebore 11 in this position. The compression spring 12 is supported by theface surface area of the armature 10 at the injection end and by a ringstep 13 of the bore 11 opposite the surface area. The spring 12surrounds with clearance a delivery plunger 14 which is fixedly, e.g.integrally connected to the armature 10 at the armature face surfacearea urged by the spring 12. The delivery plunger 14 plunges relativelydeeply into a cylindrical fuel delivery space 15 configured coaxially inthe axial elongation of the bore 11 in the pump body 8 and iscommunicatingly connected to the pressure line 2. Due to the plungingdepth pressure losses can be avoided during the sudden increase inpressure, whereby the machining tolerances between plunger 14 and barrel15 may be relatively large, e.g. merely needing to be in the range ofhundredths of a millimeter so that the machining expense is slight.

Arranged in the suction line 4 is a check valve 16. Located in the body17 of the valve 16 is a ball 18, for instance, as the valve elementwhich in its resting position is urged by a spring 19 against its valveseat 20 at the reservoir end of the valve body 17. For this purpose thespring 19 is supported, on the one hand, by the ball 18 and, on theother, by the wall of the body 17 opposite the valve seat 20 in theregion of the port 21 of the suction line 4.

The stop element 6 comprises e.g. a two-part housing 22 in the space ofwhich a diaphragm 23 is tensioned as the element to be displaced, thisdiaphragm separating a space filled with fuel at the pressure line sidefrom the cavity and which in the relaxed condition separates the cavityinto two halves, sealed off from each other by the diaphragm. At theside of the diaphragm facing away from the conductor 7 a spring force,e.g. a spring 24 engages a vacant space, the storage volume. This spring24 charging this storage volume is fitted as a return spring for thediaphragm 23, it being mounted by its end opposite the diaphragm on awall of the cylindrical flared cavity. The empty cavity of the body 22is defined by an arched wall forming a stop surface area 22a for thediaphragm 23.

The coil 9 of the pump 1 is connected to a control means 26 serving toelectronically control the injection device.

When the coil 9 is non-energized the armature 10 of the pump 1 is incontact with the bottom 11a due to the preloading of the spring 12, thefuel supply valve 16 is closed and the storage diaphragm 23 ismaintained by the spring 24 in its position out of contact with the stopsurface area 22a in the body cavity.

When the coil 9 is signalled via the control means 26 the armature 10and thus the plunger 14 is moved against the force of the spring 12 inthe direction of the injector 3, the delivery plunger 14 in connectionwith the armature 10 displacing fuel from the delivery barrel 15 intothe space of the stop element 6. The spring forces of the springs 12, 24are designed relatively soft so that fuel displaced by the deliveryplunger 14 forces the storage diaphragm 23 into the empty spacepractically with zero resistance during the first partial stroke, as aresult of which the armature 10 is initially accelerated almost free ofany resistance until the storage volume or empty space volume of thestop element 6 is exhausted by the diaphragm 23 coming up against thearched wall 22a. This results in fuel displacement being suddenly haltedand the fuel being abruptly compressed by the already high kineticenergy of the delivery plunger 14.

The kinetic energy of the armature 10 and the delivery plunger 14 actson the fluid, resulting in a pressure impulse which travels through thepressure line 2 to the injector 3 where it causes fuel to be ejaculated.

To end delivery the coil 9 is de-energized. The armature 10 is movedback to the bottom 11a by the spring 12, the amount of fuel stored inthe storage means 6 being sucked back into the delivery barrel 15 viathe lines 7 and 2, and the diaphragm 23 forced back into its startingposition due to the effect of the spring 24. At the same time the fuelsupply valve 16 opens so that fuel is replenished by suction from thetank 5.

Expediently arranged in the pressure line 2 between the injector 3 andthe branches 4, 7 is a valve 16a which maintains a standing pressure inthe space at the injector side which is e.g. higher than the vaporpressure of the fluid at the maximum occuring temperature so thatbubbles are prevented from forming. The standing pressure valve may beconfigured e.g. like the valve 16.

The energizing or coil current i_(sp) through the energizing coil 9results in a stroke s of the armature 10 or delivery plunger 14 which isstaggered in time relative to the start of the energizing current. Thebuild-up in the injection pressure p occurs in turn staggered in timerelative to the stroke s, namely not before displacement of the fuel issuddenly halted, and the fuel is abruptly compressed due to the alreadyhigh kinetic energy of the delivery plunger 14 (FIG. 4).

The integral of the energizing current i_(sp) with time is roughlyproportional to the amount of fuel ejected per injection pulse, theleading edge 95 of the energizing current i_(sp) having a substantialeffect on initiation of the injection pressure p since the leading edge95 initiates acceleration of the armature 10 or delivery plunger 14. Dueto the fluctuations of the leading edges of the energizing currentpulses 94 as described at the outset in known methods for signalling theenergizing coil, more particularly in a pump-injector system,considerable differences thus materialize in the amount of fuelejaculated per injection pulse for an identical pulse length and thesame maximum current strength of the current setpoint curve.

Furthermore, for a predetermined constant energizing current i_(sp) theforce exerted by the armature depends on the so-called working air gapwhich is proportional to the working stroke of the armature. Theexponential function profiles of the force exerted by the armature as afunction of the working air gap 1 greatly differ, depending on thegeometry of the reciprocating plunger pump employed, more particularlyas regards the armature, the coil or the surroundings thereof. In FIG.5, I denotes a function of the force F exerted by the armature depondingon the working air gap 1 which is typical for the fuel injection deviceas illustrated in FIG. 3. This function may also exhibt, however, atotally different profile, e.g. a gradually rising profile, denoted byII in FIG. 5.

By means of the method in accordance with the invention a currentsetpoint curve can be set adapted to such special framework conditions,as given, for example, by the F-1 dependency (FIG. 7) whereby thecurrent setpoint curve features a leading edge 100 which graduallyincreases, attains an arched maximum 101 before gradually decreasing bythe trailing edge 102. The trailing edge 102 may drop off abruptly as ofa certain point in time 103. The important thing is that the curve onlycauses changes in the energizing current i_(sp) which lie within thecontrol range of the current control circuit employed so that it isassured that the energizing current obeys the set current setpointcurve. The gradually decreasing trailing edge 102 in the pulse profileillustrated by way of example in FIG. 7 is adapted to the force(F)/working air gap (1) function denoted I in FIG. 5 since as of acertain working stroke of the armature 10 or as of a certain working airgap 1 a high current prompts only an unsubstantial acceleration at thearmature so that a high current would result in minor utilization of theenergy supply which would be substantially converted into waste heat.The profile of the current setpoint curve is, however, not restricted tothis special more-or-less bell-shaped configuration, it instead to beadapted individually to the reciprocating plunger pump and the geometrythereof employed in each case, i.e. selected so that for a minimum inputof electrical energy a maximum delivery output or flow is achieved foreach injection pulse.

Producing the current setpoint curve 90 with a microprocessor mayinvolve significant computation, especially at high speeds. This is whyit may be expedient to provide an analog setpoint control circuit (FIG.8) which generates a pulse-shaped current setpoint curve having apredetermined profile, preferably in the form of an exponentialfunction, for instance, as a function of a square-wave pulse signal 110and a reference voltage 111. Such a circuit comprises, for example, aresistor 112 and a capacitor 113 and a switch 114 which is generallyachieved by a transistor. Applied to the resistor 112 on one side (pointB) is the reference voltage 111 whilst the other side of the resistor112 is connected to one side of the capacitor 113. The capacitor 113 isgrounded by its side remote from the resistor 112, it being connected tothe connecting lead between the resistor 112 and the capacitor 113 andthe grounded side of the capacitor 113 so that it short-circuits thecapacitor 113 in the closed condition. For ON/OFF control of the switch114 the square-wave pulse signal 110 is applied (point A). The currentsetpoint curve of the set voltage is tapped from the connecting leadbetween the resistor 112, the capacitor 113 and the switch 114 at pointC. Point C is connected to the current control circuit, for example, tothe non-inverting input of the comparator 603 of the circuit as shown inFIG. 1.

When the switch 114 in this setpoint control circuit is closed thecapacitor 113 discharges abruptly and no voltage is applied to point C.On opening the switch 114 the capacitor 113 is gradually charged via theresistor 112, this charging voltage being tapped from point C as thecurrent setpoint curve (set voltage). The profile of the voltage rise isdictated by the RC pad 112, 113 as an exponential function. The rate ofslope of rise of the current setpoint curve tapped from the point C isproportional to the level of the reference voltage applied to point B,this voltage forming the base value U0 in the equation (2). The pulselength is dictated solely by the width of the pulses forming thesquare-wave pulse signal 110, the length of the pulse of the currentsetpoint curve being dictated by OFF action of the switch 114, since inthe OFF condition of the switch 114 the set voltage for the currentsetpoint curve is tapped from point C. The length of the OFF pulse ofthe square-wave control pulse signal 110 thus dictates the length of theenergizing current pulse.

By the simple means of this setpoint control circuit a current setpointcurve is generated with pulses in the form of an exponential function,the pulse length of which and their rise can be controlled independentlyof each other, the profile of the current setpoint curve as a wholecorresponding to an exponential function. The current setpoint curve canbe adapted to the energizing coil current curve 92 which features themaximum rise in current limited by the mutual induction for the minimumvoltage available at the energizing coil so that the current setpointcurve is in the control range of the current control circuit and amaximum amount of fuel can be injected precisely metered.

The corresponding adaptation, implemented in general by the referencevoltage 111 (U₀), need not be permanently corrected. Instead it may beadapted in time spacings corresponding to one revolution of the engineto which changes in the engine condition are adapted, thus considerablyfacilitating the control means to be used.

The set current control circuit is not limited to the embodiment asdepicted in FIG. 8. Instead it may be varied in arrangement or in thenature of its components. Thus, use can be made of a variable resistor112 or a variable capacitor 113 so that the reference voltage 11 canremain constant. The resistor 112 or capacitor 113 may be replaced by anactive comparator. The set voltage 111 may also be represented by a setcurrent, for example, by means of a RL pad, the set current being tappedvia a resistor.

At the end of each energizing current pulse 94 the energizing current 91and the magnetic field produced thereby collapses since the energizingcoil circuit is opened, and thus the end of the energizing current pulsehas no effect significantly influencing the amount of fuel per injectionpulse.

The method in accordance with the invention is not solely dedicated tometering the amount of fuel, it instead assuring that an ejaculatedamount of fuel is made available reproducibly and irrespective ofexternal influencing factors such as voltage and temperature. The amountof fuel is principally set for a specific setpoint profile of thesignalling curve over the time duration of the current pulse.

What is claimed is:
 1. A method for signaling an energizing coil of asolenoid-operated reciprocating plunger pump employed as a fuelinjection device, in which the energizing coil is energized via acurrent control circuit pulsed at high-frequency by an energizingcurrent and each pulse causes an impulse movement of an armature drivenby the energizing coil, and said current control circuit controls saidenergizing current flowing through said energizing coil as a function ofa current setpoint curve, said method comprising the steps of:formingeach pulse of said current setpoint curve with a gradually risingleading edge resulting in a corresponding gradually rising leading edgeof said pulse of said energizing current in said energizing coil; andcontrolling said current setpoint curve so that said energizing currentdoes not change faster than the maximum change in current possible forthe minimum voltage available at said energizing coil and limited due tomutual induction.
 2. The method as set forth in claim 1 furthercomprising the step of controlling said gradually rising leading ledgeof said current setpoint curve by a profile corresponding to anexponential function.
 3. The method as set forth in claim 1 furthercomprising the step of sensing an engine speed and/or a temperatureexisting as said energizing coil to adapt said current setpoint curve tothe voltage available at said energizing coil.
 4. The method as setforth in claim 1 further comprising the step of computing said currentsetpoint curve by a microprocessor and applying said computed setpointcurve to said current control circuit.
 5. The method as set forth inclaim 1 further comprising the steps of:generating said current setpointcurve with a digital/analog converter; and coupling said setpoint curveto said current control circuit as a setting voltage.
 6. The method asset forth in claim 1 further comprising the step of forming each pulseof said current setpoint curve as an exponential function over its fullpulse profile.
 7. The method as set forth in claim 1 further comprisingthe step of adapting said current setpoint curve to a reciprocatingplunger pump having a force (F)/working air gap (1) function that isbell-shaped.
 8. The method as set forth in claim 1 further comprisingthe steps of:generating the profile of said current setpoint curve bymeans of a setpoint control circuit; forming said setpoint controlcircuit with an RC pad including a resistor and a capacitor; andcharging said capacitor via said resistor in regular time intervals toproduce a pulse-shaped current setpoint curve corresponding to anexponential function.
 9. The method as set forth in claim 1 furtherincluding the steps of:controlling the pulse length and rise of saidpulses of said current setpoint curve independently of each other by asquare-wave pulse signal being applied to a switch; short-circuitingsaid capacitor with said switch; and applying a variable referencevoltage in the form of said square-wave pulse signal to said capacitorvia said resistor when said switch is open.
 10. The method as set forthin claim 1 further comprising the step of using a pump-injector deviceoperating in accordance with the solid-state energy storage principle asthe fuel injection device.